The present invention relates to a software portable telephone set and, more particularly, to a software portable telephone set capable of coping with a plurality of different radio systems with the same hardware structure by emitting reconfiguration afresh and also mounting and demounting for each system.
In a software radio unit, signals which are received and to be transmitted are converted in an A/D and D/A converters from analog to digital signal and vice versa, respectively, so that digital signal processing is performed as much as possible in the radio unit. Digital signal processing is performed according to a software program. This means that the content or function of the signal processing can be changed by replacing the software. It is thus possible to readily cope with a plurality of different radio systems with the same hardware structure by changing programs.
However, when it is intended to apply such software radio techniques to portable telephone sets, the following problem is encountered. To be able to cope with a plurality of different systems, wide-band active and passive components are necessary. Usually, the expanding the frequency band coverage of components results in characteristics deterioration.
Particularly, deterioration of the transmission side characteristics due to frequency band coverage increase directly influences the performance of the portable telephone set, and this is a great barrier in the realization of software portable telephone sets.
While the above software radio techniques require wide-band passive and active components to be able to cope with a plurality of different systems. Usually, the characteristics of the active and passive components are deteriorated with frequency band coverage increase. Particularly, it is really difficult to maintain high efficiency of a transmitting power amplifier, which is one of the main function components of the transmitting side part, over a wide frequency band. It is also really difficult to increase, with low loss, the frequency band coverage of transmission signal filters and isolators. Deterioration of characteristics of the transmission side components poses problems in the portable telephone set that allowed time of use is reduced and that the size of the portable telephone set body is increased, thus greatly spoiling the commercial value of the software portable telephone set.